Many products of commerce are temperature sensitive and may spoil, deteriorate or lose quality if they suffer even brief exposure to a temperature near or below freezing. For example, bananas turn brown and become mushy. Some flowers, salad greens and herbs, such as basil, wilt, shrink and become dark colored, useless and/or unappealing when exposed to freezing or near-freezing temperatures. Such changes are well known and are largely caused by ice crystals destroying the integrity of the botanical cells.
Many important commercial products, additional to the above, are susceptible to comparable freeze-induced damage, for example, other food and food products, certain pharmaceuticals including some drugs, sera and vaccines, as well as some industrial chemicals, and other products, as will be known or apparent to those skilled in the art. Some examples of commercially significant freeze-sensitive products include freeze-sensitive liquid vaccines such as those employed in the World Health Organization (“WHO”) Extended Program of Immunization.
One way of addressing this problem is to indicate irreversibly that an individual item, packet, syringe, vial, bottle or other volume container has been subjected to deleterious freezing conditions.
A variety of proposals are known for providing irreversible indications of freeze exposure. For example, Ignacio, et al. U.S. Pat. No. 5,239,942, discloses a freeze indicator comprising a frangible ampoule which is rupturable to release a dye that provides a color change. Shahinpoor U.S. Pat. No. 6,837,620, assigned to JP Labs, Inc., discloses a shape memory alloy temperature sensor having an alloy element that changes shape when exposed, even temporarily, to temperatures below a particular start temperature to provide a persistent indication of the temperature exposure. Also, Patel U.S. Pat. No. 6,472,214 discloses a freeze monitoring device comprising a color changing indicator, which may be a partially polymerized diacetylene and can undergo an irreversible color change, e.g., from blue to red, when the activator mixture is frozen in the region of about 0 to −30° C.
Hanlon et al. in U.S. Pat. No. 4,148,748 (“Hanlon”) disclose a nonreversible freeze-thaw indicator intended to detect whether an article has been subjected to freezing or thawing conditions. Hanlon's indicator employs a colloidal dispersion of organic solid particles of a polymeric resinous material, which may be in latex form, for example, styrene polymers. Various other styrene, vinyl and vinylidine polymers and copolymers are mentioned. Hanlon's colloidal dispersions are reported to become nonreversibly destabilized upon freezing, transforming a translucent dispersion to a substantially opaque dispersion. Typically a latex dispersion may have the appearance of a low-fat milk. Once frozen and thawed the resultant product may have the appearance of frozen milk that has curdled or gelled.
Pursuant to the present invention, the indicator described by Hanlon is believed to lack adequate shelf life for some applications and may respond inconsistently to temperatures in the freezing range, giving a poor or nonexistent visual signal.
Various freeze indicators are known that utilize the expansion of water on freezing to rupture a container. For example, Johnson U.S. Pat. No. 4,191,125 discloses a freeze indicator which includes a frangible ampoule substantially filled with a mixture of water, a nucleating agent, and a surfactant. Upon reaching the freezing point of water, the water mixture freezes, fracturing the frangible ampoule. According to Johnson: a nucleating agent can be used to overcome what is called an undercooling effect; a dye-printed pad can be employed to show a color change; and deuterium oxide may be added to raise the freezing point.
Emslander et al. U.S. Pat. No. 4,846,095 discloses a freezing point indicating device comprising a microporous sheet which is wetted by a freeze-sensitive mixture of at least two liquids e.g. a water/butanol mixture. When the temperature of the liquid mixture reaches a critical value, such as the freezing point of water, the optical properties of the microporous sheet are changed.
Pereyra U.S. Pat. No. 5,964,181 discloses a critical temperature indicating device employing an indicating composition. The indicating composition is described as including: an organic compound that has a freezing point above the critical temperature; a compound that has a freezing point below the critical temperature; and a wetting component that can wet out a microporous membrane at about the critical temperature upon solidification of a portion of the composition. According to Pereyra, the wetted membrane is rendered generally irreversibly transparent, translucent, or with colorant therein. The device can employ barrier materials to provide a barrier to water vapor, environmental gases, etc., such that they do not contaminate the indicating composition in the device. Pereyra discloses that a change in opacity and/or color of the microporous membrane indicates that the temperature has dropped to, or below, the critical temperature to be indicated. Also described is that the indicator composition can be a solution or a gel. Furthermore, immobilizing agents such as thickeners and viscosifiers can be added to the composition to control the rate of diffusion and/or build viscosity.
Patel U.S. Pat. No. 6,472,214 discloses a device composed of a color changing indicator, an optional polymeric binder, that can have gel-forming capability, and a solvent mixture which induces a color change in the indicator when the device is frozen, in the region of about 0 to −30° C. The color-changing indicator can be a fine dispersion of a partially polymerized diacetylene dispersed in the solvent mixture. When the temperature of the device is lowered to the freezing point of water, an activator solvent phase separates out of the solvent mixture and induces a color change in the indicator.
Guisinger U.S. Pat. No. 6,957,623 describes a critical temperature indicator which produces a visual, irreversible indication that the indicator has been exposed to a critical temperature such as a temperature near the freezing point of water. As described, Guisinger's critical temperature indicator includes a transparent housing and a temperature sensitive transformable material contained within the transparent housing. The transformable material includes mixture of water, a nucleating agent, latex, and a stabilizer for the nucleating agent. The material is described as being translucent prior to exposure and as being transformed to be opaque. The latex is employed in an amount of from about 5 to 35% by weight and the nucleating agent is preferably an ice nucleating active (INA) microorganism.